What are the differences between deionized water and other types of purified water?
Deionized water is a kind of purified water. In the US, FDA bottled-water rules say purified water is produced by distillation, deionization, reverse osmosis or another suitable process and meets the US Pharmacopeia definition. When it was made by deionization, the label may say "deionized water"; distillation gives "distilled water" and reverse osmosis gives "reverse osmosis water".
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In this article
- Is deionized water the same as purified water?
- What methods make purified water?
- What can the label say?
- What about demineralized water?
- Which one should I use?
- Is deionized water the same as demineralized water?
- How do deionized, distilled and reverse osmosis water differ?
- Does the process name tell you how pure the water is?
Is deionized water the same as purified water?
Not exactly. “Purified water” is the umbrella name. Deionized water is purified water made by one specific method, deionization. So deionized water counts as purified, but purified water is not always deionized.
What methods make purified water?
Under FDA’s bottled water standard (21 CFR 165.110), purified water is water produced by distillation, deionization, reverse osmosis or other suitable processes, and it must meet the definition of purified water in the United States Pharmacopeia, 23rd Revision, January 1, 1995. The regulation points to that definition rather than repeating it.
What can the label say?
- Deionized water: allowed if the water was processed by deionization.
- Distilled water: allowed if it was produced by distillation.
- Reverse osmosis water: allowed if it was processed by reverse osmosis.
What about demineralized water?
The FDA text we read does not use that name. We found no official source in this check that states whether demineralized and deionized water are the same, so we do not claim it. Ask the supplier which process was used and which grade the product meets.
Which one should I use?
The FDA rule covers bottled drinking water. For lab, medical, battery or appliance use, follow the grade the instructions name, and ask a pharmacist or the manufacturer if unsure.
Is deionized water the same as demineralized water?
Yes, as the terms are used in the sources we read. A US National Institutes of Health technical paper says “deionization (DI), demineralization or ion exchange” removes ions from feed water using synthetic resins. A correction to the text above: the FDA bottled-water rule (21 CFR 165.110) does use the name. Water that meets the purified water definition may be called “purified water” or “demineralized water”.
How do deionized, distilled and reverse osmosis water differ?
- Distilled: water is heated to boiling and collected. The NIH paper says it can remove a wide range of contaminants, but stored distillate can pick up contaminants from its container.
- Reverse osmosis (RO): a membrane process. NIH says RO membranes reject bacteria, pyrogens, and inorganic and some organic solids, but dissolved gases are not as well removed.
- Deionized: ion-exchange resins remove ions. NIH says DI does not remove particles, pyrogens or bacteria, has very limited effect on many organics, and resin beds can harbor microbial growth.
Does the process name tell you how pure the water is?
Not alone. The NIH paper says process names such as RO, DI or distilled do not by themselves define the quality needed, and that standards such as ASTM D1193 and ISO 3696 set grades. It describes USP purified water as including conductivity, organic carbon and microbial parameters. These are laboratory sources; for drinking water the FDA rule above applies.
People also ask
Is purified water the same as deionized water?
Not always. Deionized water is purified water made by deionization. FDA rules also allow distillation, reverse osmosis or other suitable processes for purified water.
What types of purified water are there?
FDA's bottled water rule names purified water made by distillation, deionization or reverse osmosis, which may be labeled distilled, deionized or reverse osmosis water.
Is demineralized water the same as deionized water?
We found no official source that says so, and the FDA rule we read does not mention demineralized water. Ask the supplier which process was used.
Is deionized water the same as purified water?
Deionized water is one kind of purified water. Under the FDA bottled-water rule, purified water can be made by distillation, deionization, reverse osmosis or other suitable processes.
Does deionized water remove bacteria?
According to an NIH technical paper, deionization does not remove particles, pyrogens or bacteria, and ion-exchange beds can harbor microbial growth.
Sources
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